1. Field of the Invention
The present invention relates to an inkjet recording apparatus including a recording head composed of a plurality of short chips arranged in the width direction of a recording medium and a rotational body for regulating the distance between the recording head and the recording medium by holding the recording medium.
2. Description of the Related Art
In general, a recording apparatus having functions of a printer, a copying machine, and a facsimile machine is configured to form images (including characters and symbols) on a recording medium, such as paper, cloth, a plastic sheet, an OHP sheet, and an envelope, based on image information. A scanning system of the recording apparatus includes serial and line types. In the serial type, images are recorded by alternately repeating main scanning that moves the recording head along the recording medium and sub scanning that feeds the recording medium at a predetermined pitch. In the line type, while one line along a direction perpendicular to the conveying direction of the recording medium (the width direction of the recording medium) being correctively recorded, images are recorded only by conveying the recoding medium (sub scanning). The recording apparatus may be classified according to the recording system into an inkjet system, a thermal transfer system, a laser beam system, a heat sensitive system, and a wire dot system.
The line-type inkjet system recording apparatus (inkjet recording apparatus) may include a long recording head (may be called as a linked-up head) configured by arranging a plurality of short chips, each having a plurality of ink nozzles, in the width direction of a recording medium. In the linked-up head, the short chips are arranged so that nozzle trains are in parallel with the width of the recording medium and so that a plurality of the nozzles covers the entire recording medium in the width direction. The linked-up head ejects ink from the nozzles of the short chips for recording on the recording medium conveyed in a direction intersecting with the arranging direction of the short chips. Such a recording apparatus may also be called a full multiple printer.
FIG. 10 is a plan view showing a schematic configuration of the linked-up head elongated by linking the short chips together. FIGS. 11A and 11B are front views showing nozzle arrangement of the adjoining short chips in the linked-up head, wherein FIG. 11A shows the arrangement of the short chips where the nozzles at the end portion of each short chip overlap with those of the adjoining short chip in the conveying direction of the recording medium; FIG. 11B shows the arrangement of the short chips where the nozzles at the end portion of each short chip do not overlap with those of the adjoining short chip in the conveying direction of the recording medium. A short chip 61 herein includes a head chip with a length of about 0.2 to 1.0 inch and having 128 to 1256 nozzles arranged in a line. The nozzle density (resolution) of this case is equivalent to 1200 dpi. By alternately arranging a plurality of the head chips 61 so that adjoining ends of each head chip overlap with each other in the conveying direction of the recording medium, a linked-up head 1 with a desired size (desired length) is configured. A recording apparatus including such a long head is designated for high speed recording in comparison with a general serial recording apparatus.
FIG. 12 is a schematic view showing the recording operation of the serial recording apparatus; FIG. 13 a schematic view showing the recording operation of the full multiple recording apparatus including the linked-up head. In the serial recording apparatus, as shown in FIG. 12, while a head 101 being moved (scanned) relative to a recording medium 51 in a direction intersecting with the conveying direction of the recording medium 51, images are formed. Whereas, in the full multiple recording apparatus, as shown in FIG. 13, while the head 1 is fixed at a predetermined position, images are formed on the recording medium 51 conveyed in a direction intersecting with the arranging direction of a plurality of nozzles 62 of the head.
A conveying unit for conveying the recording medium in the full multiple recording apparatus includes an electrostatic absorption-transportation belt type in that the recording medium is absorbed on a belt with an electrostatic force and an air suction conveying type in that the recording medium is conveyed by absorbing it with an air suction force. It is very important for forming high quality images to have a distance between the heat and the recording medium (also referred to a head recording medium distance below). Namely, with reducing head recording medium distance, the accuracy is improved in landing positions on the recording medium of ink droplets ejected from the head. Hence, an image forming section has been designed such that the head approaches the recording medium as close as possible by eliminating the floating up of the recording medium by providing a rotational body for holding down the recording medium on a conveying belt, such as a spur roller and a roller.
FIG. 14 is a plan view showing conventional arrangement of rotational bodies for holding down the recording medium. Referring to FIG. 14, rotational bodies 152, such as spur rollers or rollers, are arranged for holding down a recording medium 51 on a conveying belt on upstream and downstream sides of the linked-up head 1 in the conveying direction. By providing these rotational bodies, the apparatus is devised such that the linked-up head 1 is moved to the recording medium 51 as closer as possible so as to prevent the deterioration in recorded image quality. Such a rotational body has been used as means for preventing the floating up of a recording medium also in the serial type inkjet recording apparatus as disclosed in Japanese Patent Laid-Open No. H07-60966.
However, as shown in FIG. 14, the use of the spur roller or the roller 152 for holding down the recording medium 51 on the conveying belt causes a region having already-formed images of the recording medium to be pushed, so that the degradation, such as flaws and coming-off, may be generated on the recording medium. Also, in the serial recording apparatus, when the recording medium is held down with the spur roller, etc., the apparatus is devised to have a time difference between the present scanning and the next scanning in accordance with image information in the vicinity of the spur roller as shown in Japanese Patent Laid-Open No. H07-60966. This is for ensuring the sustainable state against the pushing with the spur roller by securing a sufficient ink drying time so that ink droplets are absorbed into the recording medium. Whereas, in the full multiple recording apparatus including the linked-up head, images are formed only by paper feeding principally for high speed recording while one line being correctively recorded, so that the countermeasure in the serial recording apparatus cannot be adopted.